The objective of this program is to develop methods for external beam radiation therapy to increase the dose to the tumor and/or to decrease radiation-induced complications in normal tissues. The means of achieving this is to use computer-controlled linear accelerators which allow versatile beam configuration and shaping. Such a system has been developed and tested. For treatment preparation, diagnostic data from various sources, including computed tomography and scintigraphy, are critically analyzed and synthesized by the radiotherapist and the physicist, aided by a computerized "Patient Data Acquisition System", which is under development. The selection of beams for the treatment is facilitated by computer graphics and rapid calculation of dose distributions. More detailed calculations are performed for documentation purposes. Methods of dose calculation are being developed to meet these two objectives, including high accuracy computations in the presence of anatomical heterogeneities. Various treatment techniques are under development, using different combinations of moving parameters. The potential benefit using a computer-controlled multi-sectioned collimator as part of the treatment delivery system is explored.